To prepare the sauce, place the whole canned tomatoes, the liquid from the tomatoes, the onion, and the garlic in a blender or food processor. Blend. Pour into a medium saucepan. Add the cayenne, salt, and tomato paste. Bring to a boil. Simmer for 5 to 10 minutes. Place 1/3 of the tortillas in the bottom of the crock pot. Spoon over 1/3 of the ground beef, 1/3 of the sauce, and 1/3 of the cheddar in layers. Repeat each layer twice more. Cover. Cook on low for 6 to 8 hours. Yields 6 servings.